The vast majority of television displays now in use employ a cathode ray tube. While great strides have been made in the development of high-quality cathode ray tubes, most still exhibit some degree of distortion. Such distortion is commonly characterized as either negative or positive distortion, depending on whether the picture elements (pixels) in the displayed image tend to bunch at the center or the edges. Negative distortion, also referred to as "pincushion distortion," results when the angle between rays radiating between the image plane and the focal plane of the cathode ray tube appears greater for the same rays radiating between the focal plane and the object plane. Conversely, positive distortion, also referred to as "barrel distortion," results when the angle between rays radiating between the image plane and the focal plane appears smaller for the same rays radiating between the focal plane and the object plane.
The amount of distortion that can be tolerated usually depends on the application for which the cathode ray tube is being employed. For some high-precision applications, even a small degree of barrel or pincushion distortion cannot be tolerated. For such applications, very optically precise cathode ray tubes are required which are costly to manufacture. Other optical systems, including illumination and lensing systems also suffer from these types of distortions.
There is a need for a technique for correcting distortion exhibited by an optical system without the need to modify the system itself.